U.S. patent number 5,734,216 [Application Number 08/564,623] was granted by the patent office on 1998-03-31 for magnet rotor for synchronous motor.
This patent grant is currently assigned to Nissan Motor Co. Ltd.. Invention is credited to Kenji Endo, Hiroyuki Hirano, Shigenori Kinoshita, Hiyoshi Yamada, Takao Yanase.
United States Patent |
5,734,216 |
Yamada , et al. |
March 31, 1998 |
Magnet rotor for synchronous motor
Abstract
A magnet rotor for a synchronous motor includes a yoke formed of
a magnetic material. A generally cylindrical permanent magnet is
disposed around the yoke magnet and has N and S poles alternately
located in the circumferential direction of the permanent magnet.
An adhesive is filled in the clearance between the outer peripheral
surface of the yoke and the inner peripheral surface of the
permanent magnet. The adhesive is hardened at a hardening
temperature, which is around a maximum temperature encountered
during operation of the motor to accomplish bonding between the
yoke and the permanent magnet. The clearance between the yoke and
the permanent magnet has a dimension L given by the following
formula: where E is a tensile elastic modulus of the adhesive;
.DELTA.L is a change amount of the clearance upon thermal expansion
or contraction; and .sigma.s is a tensile stress applied to the
adhesive.
Inventors: |
Yamada; Hiyoshi (Iwakura,
JP), Kinoshita; Shigenori (Kawasaki, JP),
Yanase; Takao (Kawasaki, JP), Endo; Kenji
(Kawasaki, JP), Hirano; Hiroyuki (Kanagawa,
JP) |
Assignee: |
Nissan Motor Co. Ltd.
(Yokohama, JP)
|
Family
ID: |
18107108 |
Appl.
No.: |
08/564,623 |
Filed: |
November 29, 1995 |
Foreign Application Priority Data
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Nov 29, 1994 [JP] |
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6-319160 |
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Current U.S.
Class: |
310/156.21 |
Current CPC
Class: |
H02K
1/2733 (20130101); H02K 1/278 (20130101); H02K
15/03 (20130101) |
Current International
Class: |
H02K
15/03 (20060101); H02K 1/27 (20060101); H02K
021/00 (); H02K 015/03 () |
Field of
Search: |
;310/156,42,43 ;29/598
;427/208.2,127 ;428/332 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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56-117567 |
|
Sep 1981 |
|
JP |
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57-206260 |
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Dec 1982 |
|
JP |
|
4-48573 |
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Feb 1992 |
|
JP |
|
Primary Examiner: Dougherty; Thomas M.
Assistant Examiner: Mullins; B.
Attorney, Agent or Firm: Foley & Lardner
Claims
What is claimed is:
1. A magnet rotor for a synchronous motor, comprising:
a yoke formed of a magnetic material and having a cylindrical outer
peripheral surface;
a generally cylindrical permanent magnet having N and S poles and
having a cylindrical inner peripheral surface, said permanent
magnet being disposed around said yoke; and
an adhesive disposed in a clearance between the outer peripheral
surface of said yoke and the inner peripheral surface of said
permanent magnet and encountering a range of temperatures during
operation of the motor, said adhesive having a hardening
temperature around a maximum temperature encountered during the
operation of the motor,
wherein said adhesive is heated to said hardening temperature and
is thereby under a tension during operation of said motor at a
temperature below said hardening temperature, and
wherein said adhesive under said tension absorbs a difference in
thermal expansion between said yoke and said permanent magnet.
2. A magnet rotor as claimed in claim 1, wherein said yoke has a
cylindrical outer peripheral surface.
3. A magnet rotor as claimed in claim 1, wherein said S and N poles
in said permanent magnet are alternately located at equal intervals
in a circumferential direction of said permanent magnet, each pole
extending in a radial direction and in an axial direction of said
permanent magnet.
4. A magnet rotor as claimed in claim 1, wherein said yoke has a
coefficient of thermal expansion higher than that of said permanent
magnet.
5. A magnet rotor as claimed in claim 1, wherein said clearance
between said yoke and said permanent magnet has a dimension L which
is given by the following formula:
where E is a tensile elastic modulus of said adhesive; .DELTA.L is
a change amount of said clearance upon thermal expansion or
contraction; and .sigma.s is a tensile stress of said adhesive;
wherein said clearance change amount .DELTA.L is given by the
following equation:
where t1 is the temperature at which said adhesive is hardened; t0
is a lowest environmental temperature in use of the motor; D is a
diameter of a section of said yoke on which the adhesive is
applied; .alpha.1 is a coefficient of thermal expansion of said
yoke; and .alpha.2 is a coefficient of thermal expansion of said
permanent magnet.
6. A magnet rotor as claimed in claim 1, wherein the poles of said
permanent magnet are formed by magnetizing a material of said
permanent magnet after hardening of said adhesive.
7. A magnet rotor as claimed in claim 1, wherein said permanent
magnet is formed of a plurality of separate pieces each having an
arcuate cross-section, the number of said pieces corresponding to
that of said poles.
8. A magnet rotor as claimed in claim 1, wherein said adhesive is
of a silicone-system.
9. A magnet rotor as claimed in claim 8, wherein said
silicone-system adhesive has a tensile elastic modulus of not
higher than 3 Kgf/mm.sup.2 and an elongation percentage of not
lower than 200%.
10. A method of producing a magnet rotor for a synchronous motor,
comprising the steps of:
providing a yoke formed of a magnetic material and having a
cylindrical outer peripheral surface;
providing a generally cylindrical permanent magnet having N and S
poles and having a cylindrical inner peripheral surface;
locating said permanent magnet around said yoke;
filling an adhesive having a hardening temperature close to a
maximum temperature encountered during operation of the motor in a
clearance between the outer peripheral surface of said yoke and the
inner peripheral surface of said permanent magnet; and
heating said adhesive to the hardening temperature to bond said
yoke to said permanent magnet,
wherein said adhesive is under tension during operation of said
motor at a temperature below said hardening temperature and thereby
said adhesive absorbs a difference in thermal expansion between
said yoke and said permanent magnet.
11. A method as claimed in claim 10, further comprising the step of
magnetizing a material of said permanent magnet to form said poles
after the step of heating said adhesive.
12. A method of producing a magnet rotor for a synchronous motor,
comprising the steps of:
providing a yoke formed of a magnetic material and having a
cylindrical outer peripheral surface;
providing a generally cylindrical permanent magnet having N and S
poles and having a cylindrical inner peripheral surface;
disposing said permanent magnet around said yoke;
determining a maximum temperature encountered during operation of
the motor;
selecting an adhesive having a hardening temperature near said
maximum temperature;
filling said adhesive in a clearance between the outer peripheral
surface of said yoke and the inner peripheral surface of said
permanent magnet; and
heating said adhesive to the hardening temperature,
wherein said adhesive is under tension during operation of said
motor below said hardening temperature and thereby said adhesive
absorbs a difference in thermal expansion between said yoke and
said permanent magnet.
13. A method as claimed in claim 12, further comprising the step of
magnetizing a material of said permanent magnet to form said poles
after the step of heating said adhesive.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to improvements in a magnet rotor for a
permanent magnet type synchronous motor.
2. Description of the Prior Art
Hitherto a magnet rotor of a permanent magnet type synchronous
motor is usually produced as follows: First, an adhesive is applied
on the outer peripheral surface of a cylindrical yoke formed of a
magnetic material. Then, the yoke with the adhesive is inserted
inside a cylindrical permanent magnet. Thereafter, the adhesive is
hardened at an ordinary temperature. A production method analogous
to the above is disclosed, for example, in Japanese Patent
Provisional Publication No. 4-48573.
A fragmentary sectional view of a bonding section of the magnet
rotor produced in the above manner is shown in FIGS. 7A to 7C in
which FIG. 7A shows the bonding section in a condition in which
adhesion has been completed at an ordinary temperature; FIG. 7B
shows the bonding section at a high temperature condition; and FIG.
7C shows the bonding section at a low temperature condition.
However, drawbacks have been encountered in the magnet rotor
produced in the above-discussed manner. That is, the adhesive is
hardened at an ordinary temperature, and therefore a thermal
expansion of the magnet rotor occurs as shown in FIG. 7B when an
environmental temperature is raised from an ordinary temperature
(around 20.degree. C.) corresponding to the adhesive hardening
temperature (t0) to a level of, for example, 120.degree. C.
corresponding to the highest temperature (t1) in use of the magnet
rotor.
At this time, a difference in expansion between the yoke and the
permanent magnet is produced in an amount of about 0.125 mm at a
temperature difference (t1-t0=120-20=10.degree. C.) as indicated at
a point A in FIG. 8 since the yoke and the permanent magnet are
different in coefficient of thermal expansion. The yoke has, for
example, a coefficient of thermal expansion of 11.4.times.10.sup.-6
in case of being formed of a material S10C, while the permanent
magnet has, for example, a coefficient of thermal expansion of
1.5.times.10.sup.-6 in case of being formed of a neodymium iron
boron (Nd--Fe--B) magnet. Additionally, the adhesive is in use
under a compressed condition since the adhesive is hardened at the
ordinary temperature. Therefore, it is necessary to absorb the
above thermal expansion difference of 0. 125 mm under deformation
of the cylindrical permanent magnet.
However, assuming that an allowable stress of the cylindrical
permanent magnet is 5.5 Kgf/mm.sup.2, the cylindrical permanent
magnet is unavoidably broken at a stage of being deformed in an
amount of about 0.1 mm, exceeding the allowable stress, as shown in
FIG. 9. Such a deformation amount of about 0.1 mm corresponds to
the expansion difference of 0.1 mm indicated at a point B.
Accordingly, the temperature difference (t1-t0) is 75.degree. C.,
so that the highest temperature in use of the rotor becomes
95.degree. C. This relationship is diagramatically shown in FIG.
10, in which the cylindrical permanent magnet reaches its
thermal-durability limit at 95.degree. C. and is unavoidably
broken.
SUMMARY OF THE INVENTION
It is an object of the present invention is to provide an improved
magnet rotor for a synchronous motor, by which drawbacks
encountered in conventional magnet rotors can be effectively
overcome.
Another object of the present invention is to provide an improved
magnet rotor for a synchronous motor, which can be effectively
prevented from being thermally damaged or broken even in use at
high temperatures.
A further object of the present invention is to provide an improved
magnet rotor for a synchronous motor, in which an adhesive disposed
between a yoke and a permanent magnet is in a tensioned condition
during use of the motor.
An aspect of the present invention resides in a magnet rotor for a
synchronous motor, which magnet rotor comprises a yoke formed of a
magnetic material and having a cylindrical outer peripheral
surface. A generally cylindrical permanent magnet is disposed
around the yoke and has N and S poles, the permanent magnet having
a cylindrical inner peripheral surface. An adhesive is disposed in
a clearance between the outer peripheral surface of the yoke and
the inner peripheral surface of the permanent magnet. The adhesive
is hardened at a temperature around the maximum temperature in use
of the motor so as to accomplish bonding between the yoke and the
permanent magnet.
Another aspect of the present invention resides in a method of
producing a magnet rotor for a synchronous motor. The method
comprises the following steps: (a) preparing a yoke formed of a
magnetic material and having a cylindrical outer peripheral
surface; (b) preparing a generally cylindrical permanent magnet
having N and S poles and having a cylindrical inner peripheral
surface; (c) locating the permanent magnet around the yoke; (d)
filling an adhesive in a clearance between the outer peripheral
surface of the yoke and the inner peripheral surface of the
permanent magnet; and (e) heating the adhesive at a temperature
around the maximum temperature in use of the motor so as to
accomplish bonding between the yoke and the permanent magnet.
According to the above magnet rotor of the present invention,
adhesion or bonding between the yoke and the permanent magnet is
accomplished by hardening the adhesive at the temperature around
the highest temperature encountered in use of the motor, and
therefore the permanent magnet can be effectively prevented from
being thermally broken thereby largely extending a temperature
range in which the rotor can be used. This renders it possible to
make the motor small-sized. Additionally, a binding operation of
the outer peripheral portion becomes unnecessary thereby reducing a
production cost.
In the present invention, it is preferable that the clearance
between the yoke and the permanent magnet has a dimension L which
is given by the following formula:
where E is a tensile elastic modulus of the adhesive; .DELTA.L is a
change amount of the clearance upon thermal expansion or
contraction; and .sigma.s is a tensile stress applied to the
adhesive;
wherein the clearance change amount .DELTA.L is given by the
following equation:
where t1 is the hardening temperature at which the adhesive is
hardened; t0 is a lowest environmental temperature in use of the
motor; D is a diameter of a section of the yoke on which the
adhesive is applied; .alpha.1 is a coefficient of thermal expansion
of the yoke; and .alpha.2 is a coefficient of thermal expansion of
the permanent magnet.
With this clearance between the yoke and the permanent magnet, a
sufficient surplus can be obtained relative to thermal breakage of
the permanent magnet due to a tensile stress of the adhesive at low
temperatures, so that a reliability in operation of the motor can
be obtained even under application of a high centrifugal force to
the permanent magnet.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded perspective view of an embodiment of a magnet
rotor according to the present invention;
FIGS. 2A to 2C are schematic fragmentary sectional views showing
the bonding states of a bonding section between a yoke and a
cylindrical permanent magnet of the magnet rotor of FIG. 1 in
various temperature conditions;
FIG. 3 is a graph showing the stress applied to the cylindrical
permanent magnet of the magnet rotor of FIG. 1 in terms of changing
temperatures;
FIG. 4A is a graph showing the relationship between the tensile
strength and the elongation percentage of an adhesive used in the
magnet rotor of FIG. 1;
FIG. 4B is a graph showing the relationship between the compressive
stress and the contraction percentage of the adhesive of FIG.
4A;
FIG. 4C is a graph showing the relationship between the tensile
stress and the elongation percentage in case of the thickness of
the layer of the adhesive of FIG. 4A being 0.2 mm;
FIG. 5 is a graph showing the stress generated in the cylindrical
permanent magnet of the magnet rotor of FIG. 1, in terms of the
inner pressure acting on the cylindrical permanent magnet;
FIG. 6 is a graph showing the centrifugal stress generated in the
cylindrical permanent magnet of the magnet rotor of FIG. 1, in
terms of the rotational speed of the magnet rotor;
FIGS. 7A to 7C are schematic fragmentary sectional views showing
the bonding states of a bonding section between a yoke and a
cylindrical permanent magnet of a conventional magnet rotor;
FIG. 8 is a graph showing the difference in thermal expansion or
contraction between the yoke and the cylindrical permanent magnet
in terms of the difference in temperature between a temperature
(t1) in use of a motor and a temperature (t0) at which the adhesive
is hardened, which is common in the embodiment of the present
invention and the conventional magnet rotor;
FIG. 9 is a graph showing the stress generated in the cylindrical
permanent magnet of the conventional magnet rotor, in terms of the
deformed amount of the cylindrical permanent magnet;
FIG. 10 is a graph showing the stress applied to the cylindrical
permanent magnet of the conventional magnet rotor, in terms of the
changing temperature; and
FIG. 11 is an exploded perspective view of a modified example of
the embodiment of the magnet rotor according to the present
invention.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring now to FIG. 1, an embodiment of a magnet rotor of a
synchronous motor, according to the present invention is
illustrated by the reference numeral R. The magnet rotor R
comprises a cylindrical yoke 1 formed of a magnetic material such
as S10C (according to Japanese Industrial Standard No. G4051). A
cylindrical permanent magnet 2 is made of neodymium iron boron
(Nd--Fe--B) magnet and coaxially disposed around or on the yoke 1,
though they are shown separate from each other in FIG. 1. The
permanent magnet 2 is provided with N and S poles each of which
extends in a radial direction and in a thickness direction of the
cylindrical permanent magnet 2. The N and S poles are alternately
located at equal intervals in a peripheral direction of the
cylindrical permanent magnet 2. The N and S poles are formed, for
example, by magnetizing the permanent magnet 2.
In this embodiment, a silicone-system adhesive (containing silicone
as a main component) having a high elongation percentage is filled
in a clearance between the outer peripheral surface of the yoke 1
and the inner peripheral surface of the permanent magnet 2. The
silicone system adhesive has, for example, a tensile elastic
modulus of not higher than 3 kgf/mm.sup.2, and an elongation
percentage of not lower than 200%. The silicone system adhesive is
hardened upon heating at a (adhesion) temperature which is around
the highest temperature (ranging from 80.degree. C. to 160.degree.
C.) encountered in use or during operation of the motor, thereby
bonding the yoke 1 and the permanent magnet 2. The elongation
percentage is a percentage of the maximum elongation of the
adhesive relative to an original length of the adhesive. In this
instance, the thickness of the layer of the adhesive is 0.2 mm. In
production of the magnet rotor R, the adhesive is filled in the
clearance between the outer peripheral surface of the yoke 1 and
the inner peripheral surface of the permanent magnet 2 after the
yoke 1 and the permanent magnet 2 are positioned coaxial with each
other. However, the adhesive may be first applied on the peripheral
surface of the yoke 1, and then the yoke 1 with the adhesive may be
inserted into the inner bore of the permanent magnet 2.
FIGS. 2A to 2C show adhesion or bonding states of a bonding section
between the yoke 1 and the permanent magnet 2 at various
temperatures, respectively. In these figures, a dash-dot line
indicates a rotational axis of the rotor R. FIGS. 2A, 2B and 2C
correspond to the adhesion states at a high temperature, at an
ordinary temperature, and at a low temperature, respectively.
Adhesion between the yoke 1 and the permanent magnet 2 is
accomplished by hardening the adhesive 3 at a high temperature
around the highest temperature in use of the motor (accordingly,
the rotor R), in which the difference between the outer diameter of
the yoke 1 and the inner diameter of the permanent magnet 2 is L.
Here, the coefficient of thermal expansion .alpha.1 of the yoke 1
is higher than that .alpha.2 of the permanent magnet 2. As a
result, a difference in thermal contraction is made between the
yoke 1 and the permanent magnet 2 at the ordinary temperature as
shown in FIG. 2B. A further large difference in thermal contraction
is made at the low temperature as shown in FIG. 2C.
Accordingly, the adhesive 3 is in use under a tensioned condition
throughout whole temperature ranges in which the motor is operated
or in use, as shown in FIG. 3.
The difference L between the outer diameter of the yoke 1 and the
inner diameter of the permanent magnet 2 is set to meet the
following equation:
where E is a tensile elastic modulus of the adhesive; .DELTA.L is a
change amount of the clearance (between the outer diameter of the
yoke 1 and the inner diameter of the permanent magnet 2) upon
thermal expansion or contraction; .sigma.s (=Pa) is a tensile
stress of the adhesive (=a pressure acting on the inner peripheral
surface of the permanent magnet 2).
The clearance change amount .DELTA.L upon thermal expansion or
contraction is given by the following equation:
where t1 is a hardening temperature at which the adhesive is
hardened to accomplish adhesion or bonding between the yoke and the
permanent magnet 2; t0 is the lowest environmental temperature in
use of the motor; D is a diameter of a section (of the yoke 1) on
which the adhesive is applied; .alpha.1 is a coefficient of thermal
expansion of the yoke 1; and .alpha.2 is a coefficient of thermal
expansion of the permanent magnet 2.
Additionally, the tensile stress .alpha.s is given by the following
equation:
where k is a value of the outer diameter of the permanent magnet /
the inner diameter of the permanent magnet; R is a value of the
outer diameter of the permanent magnet / an average diameter [=(the
outer diameter+the inner diameter) / 2)] of the permanent magnet;
and .sigma..theta. is an allowable stress of the permanent
magnet.
Next, a concrete example of the above embodiment magnet rotor
according to the present invention will be discussed.
Assuming that the rotor of the embodiment is in use within a
temperature range of from -30.degree. C. to 120.degree. C., a
temperature difference (t1-t0) is 150.degree. C. Additionally,
assuming that the adhesive-applied section diameter D is 130 mm,
the thermal expansion coefficient .alpha.1 of the yoke 1 is
11.4.times.10.sup.-6 while the thermal expansion coefficient
.alpha.2 of the permanent magnet 2 is 1.5.times.10.sup.-6, the
clearance change amount .DELTA.L upon thermal expansion or
contraction corresponds to a point C indicated in FIG. 8 and takes
the following value: ##EQU1##
FIGS. 4A, 4B and 4C depict a characteristics of the adhesive 3, in
which FIG. 4A shows the relationship between the tensile stress and
the elongation percentage; FIG. 4B shows the relationship between
the compressive stress and the contraction percentage; and FIG. 4C
shows the relationship between the tensile stress and the
elongation percentage in case that the thickness of the layer of
the adhesive 3 is 0.2 mm. These lead to the fact that the tensile
elastic modulus E of the adhesive 3 is 0.2 Kgf/mm.sup.2.
In case that the tensile stress .sigma.s of the adhesive 3 (i.e.,
the inner pressure Pa acting on the inner peripheral surface of the
permanent magnet 2) is not higher than about 0.33 Kgf/mm.sup.2, the
stress generated in the permanent magnet 2 is at a value not higher
than the allowable stress 5.5 Kgf/mm.sup.2 and therefore the
permanent magnet 2 cannot be broken, as seen from FIG. 5. At this
time, the clearance L (between the yoke 1 and the permanent magnet
2) to be filled with the adhesive 3 is not smaller than 0.12 mm
(L.gtoreq.0.12 mm).
The embodiment of the magnet rotor of the present invention is
arranged as discussed above, adhesion or bonding between the yoke 1
and the permanent magnet 2 is accomplished at a temperature around
the highest temperature in use of the motor. Accordingly, a surplus
to the allowable stress of the cylindrical permanent magnet can be
made as shown in FIG. 3, and therefore the magnet rotor can be
continued to be safely used without anxiety even upon application
of a high centrifugal force or stress as shown in FIG. 6.
Additionally, it will be appreciated that troubles such as
demagnetization (or reduction in magnetic force) can be prevented
by accomplishing magnetization of the magnet rotor after operation
of application of the adhesive 3 during production of the magnet
rotor.
While only the one-piece type cylindrical permanent magnet has been
shown and described as a permanent magnet, it will be understood
that the permanent magnet 2 may be formed of a plurality of
separate pieces (each having an arcuate cross-section) 2a, 2b whose
number corresponds to the number of poles, as shown in FIG. 11 in
which the adjacent pieces 2a, 2b have respectively a N pole and a S
pole.
* * * * *